Method of viscous oil recovery through hydraulically fractured wells

ABSTRACT

This specification discloses a method of producing viscous hydrocarbons from a subsurface formation having a preferred vertical fracture orientation. An injection well and a production well are provided which extend from the surface of the earth and communicate with the subsurface formation. The injection and production wells are spaced laterally one from the other a predetermined distance measured in a direction about normal to the preferred vertical fracture orientation and are fractured by hydraulic fracturing techniques to create vertical fractures within the formation which communicate with each well. The vertical fractures extend into the formation and follow essentially the preferred vertical fracture orientation of the formation. A thermal recovery technique is initiated and a hot fluid is injected into the fracture which extends from the injection well and viscous hydrocarbons flow from the formation into the fracture which extends from the production well and are produced via the production well to the surface of the earth.

United States Patent [1 1 Fitch et a1.

[ METHOD OF VISCOUS OIL RECOVERY THROUGH HYDRAULICALLY FRACTURE WELLS [75] Inventors: John L. Fitch, Dallas; Malcolm K.

Strubhar, Irving. both of Tex.

[73] Assignee: Mobil Oil Corporation, New York C ity, NY.

[22]- Filed: Mar. 15, 1973 [21] Appl. No.: 341,431

Closmann 166/272 X [451 May 14, 1974 Primary Examiner-David H, Brown Attorney, Agent, or Firm-A. L. Gaboriault; Henry L. Ehrlich [57] ABSTRACT This specification discloses a method of producing viscous hydrocarbons from a subsurface formation having a preferred vertical fracture orientation. An injection well and a production well are provided which cxtend from the surface of the earth and communicate with the subsurface formation. The injection and production wells are spaced laterally one from the other a predetermined distance measured in a direction about normal to the preferred vertical fracture orientation and are fractured by hydraulic fracturing techniques to create vertical fractures within the formation which communicate with each well. The vertical fractures extend into the formation and follow essentially the preferred vertical fracture orientation of the formation. A thermal recovery technique is initiated and a hot fluid is injected into the fracture which extends from the injection well and viscous hydrocarbons flow from the formation into the fracture which extends from the production well and are produced via the production well to the surface of the earth. I

5 Claims, 1 Drawing Figure -1 METHOD OF VISCOUS OIL RECOVERY THROUGH HYDRAULICALLY FRACTURED WELLS BACKGROUND OF THE INVENTION This invention is directed to a thermal method of recovering viscous hydrocarbons from a subsurface formation havinga preferred fracture orientation. More specifically, this invention is directed to a thermal recovery method wherein at least two wells extend from the surface of the earth into a subsurface formation containing viscous hydrocarbons, and vertical fractures are extended into the formation from each well.

In U. S. Pat. No. 3,221,813 there is described a technique for the recovery of viscous petroleum materials wherein an injection well and a production well are located at spaced locations with respect one to the other and are completed in a formation. A fracture is extended through the formation to establish fluid communication between the production and injection wells. A hot gas is pumped into the fracture at a pressure that is less than the fracturing pressure but sufficient'to force fluid to flow through the fracture to the production well. When the pressure rises too close to the fracturing pressure, pumping of the hot gas into the fracture is terminated and a vapor-free liquid capable of entraining viscous petroleum materials is pumped into the fracture to remove the viscous petroleum materials that have accumulated in the'fracture. After the petroleum materials have been removed, the pumping of the vapor-free liquid is terminated and the pumping of the hot gas is resumed. These steps are repeated in recovering viscous tarlike petroleum materials from the formation. In U. S. Pat. No. 3,399,721 there is described a technique for the recovery of viscous hydrocarbons from a subterranean formation employing forward in situ combustion. In accordance with this technique a horizontal fracture is extended between first and second spaced wells in the formation. Thereafter, this fracture is utilized in conjunction with an in situ combustion process for recovering viscous hydrocarbons from the formation.

In U. S. Pat. No. 3,501,201 there is described a method of recovering shale oil from anoil shale formation by extending at least-a pair of wellbores into at least one layer of water-soluble minerals disposed in the formation and forming generally vertical fractures .extending along parallel paths from each of the boreholes. Hot fluid is injected through at least one of the wellbores until flow into at least one of the fractures therein is thermallyclosed .by swelling shut the walls of the fracture. Fluid in at least one borehole in which at least one fracture has been thermally closed is pressurized until at least one new fracture is formed and the steps of injecting hot fluid and pressurizing of fluid are repeated at successively higher temperatures and pressures until the resulting fractures form a channel interconnecting the wellbores through which fluid can flow from one wellbore to another. The walls of the fracture interconnecting the' wellbores are leached at a controlled temperature until the channels provided between the wellbores are capable of remaining open while hot fluid is circulated between the wellbores.

SUMMARY OF THE INVENTION This invention is directed to a method of recovering viscous hydrocarbons from a subsurface formation having a preferred vertical fracture orientation. At least an injection well and a production well are extended into and communicate with the formation. The injection and production wells are spacedlaterally one from the other a predetermined distance measured in a direction normal to the preferred vertical fracture orientation. Hydraulic pressure is applied via the injection well to the formation and a first vertical fracture is formed which extends into the formation in the direction of the preferred vertical fracture orientation. Hydraulic pressure is also applied via the production well to the formation and a second vertical fracture is formed and propping material is deposited therein to maintain open the second vertical fracture. The first vertical fracture is maintained open and a heated fluid is injected via the injection well into the first vertical fracture to displace the viscous hydrocarbons from the formation intermediate the first and second vertical fractures toward the second vertical fracture communicating with the production well. Concomitantly with the flow of heated fluid into the injection well and the first vertical fracture the viscous hydrocarbons are produced from the formation via the second vertical fracture and the production well.

In accordance with further embodiments, the pressure in the vertical fracture which communicates with the production well is maintained at a pressure lower than the pressure in the formation surrounding this fracture. Steam is injected into the injection well and the vertical fracture communicating therewith and flowed through the formation and breaks through into the vertical fracture communicating with the production well. Steam injection is continued via the injection well and thesteam is produced from the vertical fracture communicating with the production well at a sufficient rate to 'maintain the pressure in the vertical fracture communicating with the production well at a pressure lower than the pressure in the formation surrounding this fracture. The vertical fracture communicating with the production well is thereby heated as is the formation on the opposite side of this fracture without in vasion of steam and associated water beyond this fracture.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a diagrammatic plan view of a pattern of wells and associated fractures illustrating the method of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS subsurface formation. The wells are spaced laterally one from the other a predetermined distance measured in a direction approximately normal to the direction of the preferred fracture orientation. Hydraulic pressure is applied to the formation via the injection well and the production well to form a first vertical fracture which communicates with the injection well and a second vertical fracture which communicates with the production well. The first and second vertical fractures extend into the formation in the direction of the preferred vertical fracture orientation, thus forming an essentially parallel vertical fracture system. Thereafter. a thermal recovery technique is employed for recovering the viscous hydrocarbons from the subsurface formation.

Referring to the drawing there is shown a diagrammatic plan view of a portion of a subsurface formation 1 containing viscous hydrocarbons therein which portion is encompassed by the enclosure 3. The subsurface formation 1 has a preferred vertical fracture orientation, the azimuthal direction of which is illustrated by the arrow 5. An injection well 7 and production wells 9 and l I extend from the surface of the earth and communicate with the subsurfaceformation 1. A vertical fracture 13 in formation 1 communicates with the injection well 7 and vertical fractures 15 and 17 communicate with the production wells 9 and 11, respectively. The vertical fractures 13, I5,'and 17 in subsurface formation 1 follow essentially the azimuthal direction of the preferred vertical fracture orientation and are essentially parallel one with the other.

In carrying out this invention, at least an injection well and a production well are provided which extend i from the surface of the earth and communicate with the subsurface formation containing viscous hydrocarbons. It is preferred that at least two production wells be provided on opposed sides of the injection well, as illustrated in the drawing. The injection and production wells as illustrated in the drawing are located laterally one from the other a predetermined distance d measured in approximately a normal direction to the communication between the subsequently produced vertical fractures via any spurious fractures which may be generated or present in the subsurface formation in a direction other than the preferred vertical fracture orientation. Desirably, the distance 4 will be not less than 10 feet andmay be as much as 360 feet. By thus avoiding any communication by way of fractures between the injection fracture l3 and the production fractures 15 and 17, a more uniform flow of heated fluid through the formation intermediate these fractures is assured. Thoughpossibly some direct communication between the injection and production fractures could be tolerated, it would definitely very greatly reduce the efficiency of this process.

The injection and production wells are provided to communicate with the subsurface formation as illustrated in the drawing. in providing these wells, their locations are normally chosen and they are drilled and completed by conventional techniques. These techniques normally include casing the well and providing openings through the casing to establishcommunication between the subsurface formation containing viscous hydrocarbons and the interior of the well. The

4 may be introduced thereinto and applied to the subsurface formation through the o'penings in the casing.

Pressure is applied to the fracturing fluid until a vertical fracture is formed in the subsurface formation and is propagated through the formation. The vertical fracture will propagate through the formation in the direction of the preferred vertical fracture orientation of the formation. Thus, as illustrated in the drawing,-a vertical fracture 13 which communicates with the injection well 7 is formed in the subsurfaceformation l and a vertical fracture 15 which communicates with the production well 9 is also formed in the subsurface formation l.

Propping material is normally injected into the injection and production fractures at the time they are formed to maintain them open and minimize the resistance to flow of fluids through these fractures. Normally it is preferred that a production well 11 be provided on the opposed side of injection well 7 from the production well 9 and a vertical fracture 17 be formed in the subsurface formation 1 and communicate with the production well 11.

After forming the fractures which communicate with the injection and production wells a thermal recovery process is carried out in the subsurface formation 1. ln carrying out the-thermal recovery process, a heated fluid is injected via the injection well 7 into the vertical fracture 13. it is desirable that the vertical fracture 13 offer very little resistance to flow within the fracture to the heated fluid which is injected thereinto. Therefore, normally, in creating the fracture 13, propping material isinjected there-into to maintain the fracture open. The fracture 13 may be maintained open however by injecting the heated fluid via the well 7 into the fracture 13 at a pressure equivalent to the parting pressure of the formation 1. Steam is often used in carrying out thermal-processes and is the preferred heated fluid to employ in carrying out this process because of its heatcarrying capacities and its ready availability at economical cost. However, other heated fluids such as hot water, hot solvents, or hot gases may also be employed. Hereafter when reference is made to employing steam it is understood that other heated fluids may also be employed. The injection of the heated fluid, e.g. steam, via the injection well 7 and the vertical fracture 13 is continued to drive the steam and associated hot water which may be injected with or condensed therefrom through the formation as indicated by the arrows from the fracture 13. The steam thus sweeps through the portion of the formation intermediate the injection and production fractures and reduces the viscosity of the viscous hydrocarbons contained in the formation, thereby greatly increasing the production of hydrocarbons from the formation intermediate these fractures.

in accordance with an embodiment of this invention, the pressure in the production fractures 15 and 17 which communicate with production wells 9 and 11 is maintained at a pressure lower than the pressure in the formation surrounding the production fractures. Thereafter, upon breakthrough of the steam and asso ciated water into the production fractures, steam injection is continued via the injection well 7 and vertical fracture l3 and the steam and associated hot water are produced from the vertical fractures 15 and 17 via the production wells 9 and 11 at a sufficient rate to maintain the pressure in the vertical fractures communicating with the production wells at a pressure lower than the pressure in the formation surrounding these vertical fractures. Thus, the vertical fractures communicating with the production wells are heated and heat flows by conduction as indicated by the wavy lines 16 beyond the fractures which communicate with the production wells. At the same time, the steam and associated hot water which flows into the vertical fractures communicating with the production well does not invade the formation beyond these vertical fractures because of the fact that the pressure in these vertical fractures is maintained at a pressure lower than that of the surrounding formation. Thus, the steam and hot water are produced from the vertical fractures via the production well along with the hydrocarbons which flow into these vertical fractures. The invasion of heat by conduction beyond the vertical fractures communicating with the production well reduces the viscosity of the viscous hydrocarbons contained in this portion of the formation thereby facilitating the flow of these hydrocarbons into the production fractures and 17 and thence their production via the production wells. The maintaining of the pressure in the vertical fractures communicating with the production well at a pressure less than the pressure in the surrounding formation ensures that no invasion of the steam and associated hot water takes place beyond the vertical fractures but at the same time ensures that heat does invade the formation beyond these fractures and thus maximize the production of hydrocarbons from this portion of the formation.

Though it is only necessary that one injection well and one production well be provided for carrying out this invention, it is highly desirable that a second production well be provided on the opposed side of the injection well from the first production well, as illustrated in the drawing By thus providing two production wells and associated vertical fractures, the efficiency of the thermal recovery process is approximately double that which would be possible with only one production well.

The preferred vertical fracture orientation in formations exists because of naturally occurring anisotropic stress distribution and planes of weaknesses in these formations. In many instances, subsurface earth forma-- tions exhibit the same preferred vertical fracture orientation as is found in surface formations. Therefore, surface measurements may be employed as a reasonably close indication of the preferred vertical fracture orientation. The preferred vertical fracture orientation may also be determined from measurements taken in wells penetrating the subsurface earth formations of interest.- For example, these measurements may be taken from the injection or production wells which communicate with the subsurface formation 1 containing viscous hydrocarbons. Impression packer surveys may be run in wells penetrating the subsurface formations of interest to determine the-fracture orientation. Borehole televiewer surveys offer a particularly good method of determining the preferred fracture orientation trends. Borehole televiewer surveys are discussed in an article by J. Zemanek et al., entitled The Borehole Televiewer A New Logging Concept for Fracture Location and Other Types of Borehole Inspection, Journal of Petroleum Technology, Vol. XXI (June 1969), pp.

We claim:

l. A method of recovering viscous hydrocarbons from a subsurface formation having a preferred vertical fracture orientation, comprising the steps'of:

a. providing at least an injection well and a production well which extend into and communicate with said formation, said injection well and said production well being spaced laterally one from the other a predetermined distance measured in a normal direction to the preferred vertical fracture orientation;

b. applying hydraulic pressure via said injection well to said formation to form a first vertical fracture which communicates with said injection well and extends into said formation in the direction of said preferred vertical fracture orientation;

c. applying hydraulic pressure via said production well to said formation to form a second vertical fracture which communicates with said production well and extends into said formation in the direction of said preferred vertical fracture orientation and depositing propping material in said second vertical fracture to maintain open said second vertical fracture;

d. maintaining said first vertical fracture open;

e. injecting heated fluid via said injection well into said first vertical fracture to displace said viscous hydrocarbons from said formation intermediate said first vertical fracture and said second vertical fracture toward said second vertical fracture; and

f. concomitantly with the flow of heated fluid into said injection well and said first vertical fracture, producing from said formation said viscous hydrocarbons via said second vertical fracture andsaid production well.

2. The method of claim 1 wherein steam is injected as said heated fluid.

3. The method of claim 2 further comprising maintaining the pressure in said second vertical fracture which communicates with said production well at pressure lower than the pressure in said formation surrounding said second fracture.

4. The method of claim 3 wherein said steam injection is continued into said first vertical fracture and said steam breaks through into said second vertical fracture and thereafter said steam is produced from said second vertical fracture via said production well at a sufficient rate to maintain the pressure in said second vertical fracture at a pressure lower than the pressure in said formation surrounding said second vertical fracture thereby heating said second vertical fracture and said formation on the opposite side of said second vertical fracture from said first vertical fracture without the invasion of said steam into said formation on said opposite side of said second vertical fracture.

5. The method of claim 4 wherein there are provided at least two production wells located on opposite sides of said injection well at said predetermined distance from said injection well measured in a normal direction to said preferred vertical fracture orientation. 

1. A method of recovering viscous hydrocarbons from a subsurface formation having a preferred vertical fracture orientation, comprising the steps of: a. providing at least an injection well and a production well which extend into and communicate with said formation, said injection well and said production well being spaced laterally one from the other a predetermined distance measured in a normal direction to the preferred vertical fracture orientation; b. applying hydraulic pressure via said injection well to said formation to form a first vertical fracture which communicates with said injection well and extends into said formation in the direction of said preferred vertical fracture orientation; c. applying hydraulic pressure via said production well to said formation to form a second vertical fracture which communicates with said production well and extends into said formation in the direction of said preferred vertical fracture orientation and depositing propping material in said second vertical fracture to maintain open said second vertical fracture; d. maintaining said first vertical fracture open; e. injecting heated fluid via said injection well into said First vertical fracture to displace said viscous hydrocarbons from said formation intermediate said first vertical fracture and said second vertical fracture toward said second vertical fracture; and f. concomitantly with the flow of heated fluid into said injection well and said first vertical fracture, producing from said formation said viscous hydrocarbons via said second vertical fracture and said production well.
 2. The method of claim 1 wherein steam is injected as said heated fluid.
 3. The method of claim 2 further comprising maintaining the pressure in said second vertical fracture which communicates with said production well at pressure lower than the pressure in said formation surrounding said second fracture.
 4. The method of claim 3 wherein said steam injection is continued into said first vertical fracture and said steam breaks through into said second vertical fracture and thereafter said steam is produced from said second vertical fracture via said production well at a sufficient rate to maintain the pressure in said second vertical fracture at a pressure lower than the pressure in said formation surrounding said second vertical fracture thereby heating said second vertical fracture and said formation on the opposite side of said second vertical fracture from said first vertical fracture without the invasion of said steam into said formation on said opposite side of said second vertical fracture.
 5. The method of claim 4 wherein there are provided at least two production wells located on opposite sides of said injection well at said predetermined distance from said injection well measured in a normal direction to said preferred vertical fracture orientation. 